1. Field of the Invention
The present invention relates to a display device using a color filter structure and a manufacturing method of such display device. In particular, the present invention relates to a color filter structure suitable for a transflective type liquid crystal display device equipped with a transmission region and a reflection region on a pixel-by-pixel basis or by a predetermined unit display region, as well as to a manufacturing method of such a color filter structure.
2. Description of the Related Art
Conventionally, a color filter has been well known that handles: first light for forming a unidirectional optical path, such that incident light from one main face side of the color filter is transmitted through the filter only once to be colored and guided to the other main face side; and second light for forming a bi-directional optical path such that incident light from the other main face side of the color filter is transmitted through the filter to be colored, and the transmitted light is reflected by means of a light reflection element or the like arranged on the one main face side, and, again, incidents to the filter and is transmitted through the filter to be colored, and then, is returned to the other main face side. This color filter is used for a so-called transflective type liquid crystal display device in which, while light modulation according to an image to be displayed on external light incident from a front side is applied, this modulation is reflected to be guided to the front side, and, while light modulation according to an image to be displayed is applied similarly to incident light caused by a backlight system from a backside, this modulation is transmitted to be guided to the same front side. The liquid crystal display of this type provides effective image display mainly by external light (ambient light) when a use environment is bright (reflection mode), and mainly by spontaneous light emission of a backlight system when the environment is dark (transmission mode).
Such a transflective type liquid crystal display device is disclosed in M. Kudo, et al., “Development of Advanced TFT with Good Legibility under Any Intensity of Ambient Light”, IDW' 99, Proceedings of The Sixth International Display Workshops, ADM3-4, pages 182-186, Dec. 1, 1999, sponsored by ITE and SID. In this device, each pixel electrode is divided into a reflection region and a transmission region. The reflection region is provided as an aluminum based reflection electrode portion coated on an acrylic resin having an irregular surface, and the transmission region is provided as an ITO (Indium tin oxide) based transparent electrode portion having a flat surface. In addition, the transmission region is arranged at a center in one rectangular pixel region and exhibits a substantially similar rectangular shape in the pixel region, whereas the reflection region is provided as a portion in the pixel area other than this rectangular transmission region and exhibits a shape such that it surrounds the transmission region. With such pixel configuration or the like, it is intended to improve the visibility.
However, in this known liquid crystal display device, the color purity of a display color varies between the transmission region and the reflection region even in the same pixel. This difference is caused by the fact that light from a backlight system and external light respectively having different optical paths from each other are colored in the same manner, and this causes quality degradation of display colors in a whole screen area.
Patent applications of inventions intending to solve such a disadvantage include Japanese Patent Application Laid-Open No. 2003-84122 (see especially FIG. 3, Claims, and paragraphs 0009, 0010, and 0030 to 0039) that has been filed by the Applicant of the present application. The color filter according to the above invention is directed to a color filter for coloring first light that exhibits a unidirectional optical path and second light that exhibits a bi-directional optical path for each pixel, the color filter having a first color portion for coloring the first light and a second color portion for coloring the second light and wherein the first color portion and the second color portion are different from each other in thickness. Further, the color filter for coloring first light that exhibits a unidirectional optical path and second light that exhibits a bi-directional optical path on for each pixel, has: a stepped layer that can be supported by a substrate, the stepped layer being made of a light transmission material patterned so that a bottom face formed in a predetermined shape corresponding to a region for transmitting the first light in one pixel and at least one recessed portion having a wall face of a predetermined height is formed; and a color layer for coloring the first light and second light, the color layer being deposited on the stepped layer and the recessed portion.
According to the above conventional color filter, the first color portion or a portion of a color layer in a region of the bottom can be thicker than a portion (second color portion) of a color layer in another region, and thus, exhibits a unidirectional optical path. Therefore, a comparatively large coloring effect is applied to first light subjected to coloring action only once, whereas a bi-directional optical path is exhibited. Therefore, a comparatively small coloring effect can be applied to second light subjected to coloring action twice. In this manner, at color purity made uniform in pixels in response to the first light and the second light, the associated color can be reproduced, thereby improving quality of color display in a whole screen area.
In the above described conventional art, while a structure for obtaining a color balance in a pixel is primarily proposed, there is no specific disclosure of how to efficiently manufacture a color filter having such a structure. Additionally, in spite of the fact that the manufacturing steps has become complicated by complicating a pixel structure in order to enable the color balancing, consideration for simplifying a manufacturing process from aspects such as actual cost and yields or the like is not given at all.
On the other hand, it is primary routine that a process in accordance with a photography technique is conventionally carried out for patterning of a black matrix in a color filter and color portions of red (R), green (G), and blue (B). This is because such black matrix and color portions must be formed in a very fine shape, and in particular, the shapes of color filters for use in display panels employed for portable devices such as portable cellular phones require very high precision. However, the manufacturing in accordance with the lithography technique requires a number of steps and photo masks, and is disadvantageous in simplification of the whole manufacturing process.
The inside of pixels is subdivided into the first color portion and the second color portion. Thus, there is a need for alignment between the first and second color portions and the above transparent electrode portion and reflection electrode portion as well as alignment between a color filter pixel region and a pixel electrode region. A pasting step between one substrate that carries the color filter and the other substrate that carries the pixel electrode must be strict and precise. This increases a burden in development and manufacturing.